Replacing Switchmaster 400 with IQE 2 channel controller

Discussion in 'Plumbers' Talk' started by Roger Donoghue, Apr 26, 2015.

  1. Roger Donoghue

    Roger Donoghue New Member

    Hi - I've bought a house with a Switchmaster 400 controller, with a seperate dial thermostat, connected to a baxi bermuda back boiler. The current controller lets you control Heating with Hot water, or Hot Water only. There is no switch for Heating only.

    (Someone elses photo..)

    http://www.diynot.com/network/flyingsparks/albums/1141/29039

    This suggests to me (from Internet reading) that I most likely have a Gravity fed partially controlled system (hence I can't have heating without hot water). The system also has an immersion tank. I can't see a three way valve anywhere but I've not explored thoroughly yet. I have two big pumps on the floor. One of them boost the water to my kitchen (I have a ground floor flat with it's own water tank), The other has 4 pipes coming out if it and is hand written labelled as the heating pump (I reckon it actually boosts water from the other end of the house). There is also an inline central heating pump (this is why I think the pump with 4 pipes is not a heating pump). This shoudl all be kind of irrelivent but it may be helpful.

    I'm looking at replacing it with the QUE 7 day 2 channel timer controller on SFX. Also Adding a thermostat to replace the existing ugly one.

    http://www.screwfix.com/p/iqe-2-channel-7-day-time-control/79342

    https://iqe.co.uk/sites/default/files/2 channel 7 day time control_installation manual_0.pdf

    Wiring should be pretty straight forward I guess? (I'm no plumber but I'm good at sparks).

    The current SM 400 has

    N
    L
    1- CH On
    2 -
    3- HW On
    4 - CH Off

    The IQE 2 channel 7 day conroller has

    N
    L
    1 - HW Off
    2 - CH Off
    3 - HW On
    4 - CH On

    So I assume I just switch the controllers and wire 1 to 4 , 3 to 3, and 4 to 2 - seems straight forward? And Just don't mess with anything else, and also, wire my new thermostat (room stat) exactly as the existing one is wired?

    Anything to look out for? (I'm guessing my current system doesn't support CH without HW at the same time? as the current controller doesn't support it)
     
  2. G&W Plumbing & Heating

    G&W Plumbing & Heating Active Member

    That's right, you need a system upgrade buddy
     
  3. Roger Donoghue

    Roger Donoghue New Member

    An update with a couple of questions. I've done the conversion, replacing the Switchmaster 400 with an IQE 2 channel controller, and a mechanical thermostat with a wireless stat.

    The IQE is running fine. It only had two control wires conneced. HW on and CH on. (plus live and neutral of course)

    It's a partial system (I've assumed) - on the orginal controller it's either HW, or CH+HW

    I removed the jumper from the back of the IQE to set this "partial" or "gravity" fed system. (I tried its as a "full" system but it didnt work properly as expected)

    HW works as expected, CH+HW works as expected.

    There is a stat on my hot water tank and the wired go into the main heating junction block.

    I replaced the stat with a Salus wireless one. On the controller I moved the mechanical stat wires over to the NO and Comnm terminals, and then supplied L & N to the Salus as it needs them.

    Again, works fine.

    One oddity which I guess I'm not used to - coming from a house with a fully pumped system - now when I switch it to HW+CH - even if the stat for the heating is off, the hot water still heats - which I get - it's waiting for the HW stat to cut out - but it seems to do this for ages. It cuts in and out frequently Is this normal?

    Secondly - what's the stat that is actually on my Baxi Bolier - marked Min - Max - a dial - what is this setting the max temperature for?
     
  4. Roger Donoghue

    Roger Donoghue New Member

    Scratch that, I've done some reading. The dial on the boiler is the boiler stat - the overall max temp for the circulating water - be it heating or water.

    My water tank has a stat on the side. I've tested it. It works. It would just be nice if it had some kind of "dampening" - i.e. not going on and off all the time. When I've got the heating on, I really don't need a constantly super hot full tank of water, but I guess with this system, all my HW goes through my tank so you have little choice and the heating stat controls the CH pump and boiler, where as the tank stat just controls the boiler.
     

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